Vehicles with direct injection engines employ various methods for mixing fuel and air in an engine cylinder. Efficient mixing increases combustion burn rate, improving combustion stability and knock suppression. Spark ignition engines may use tumble flow motion to generate turbulence, which includes rotational motion generally perpendicular to the cylinder axis to improve air and fuel mixing. Depending on operating conditions, more or less tumble flow may be advantageous.
U.S. Pat. No. 5,718,198 provides one example approach to regulate tumble flow using a slide plate midway through each of a plurality of intake runners. The slide plate includes a plurality of holes with a size and shape complementary to those of a cross section of each intake runner. The slide plate is moved up and down to simultaneously regulate the amount/velocity of air flow through all of the intake runners by partially blocking air flow or permitting full air flow. For example, for high load and/or engine speed, the slide plate is aligned with the intake runners so that air passages are fully open and airflow is not blocked. In another example, during slow idle, the slide plate is moved into a position where the intake runners are only open partially along the top of the runners. This creates an off-center opening along the top of the air passages and causes the air flowing through the openings to begin a tumbling type of airflow pattern.
The inventors herein recognize potential issues with such a configuration for generating tumble airflow. As one example, when the slide plate is partially closed, air traveling through the intake runner may impact the abrupt wall of the slide plate as the airflow changes direction in order to pass through the opening. Such an approach may create significant flow resistance and unnecessarily reduce the velocity of air as it travels from the intake side of the slide plate to the cylinder side of the slide plate. As a second example, because of the vertical motion of the plate, the engine must accommodate space for the slide plate both above and below the intake runners. In compact engine designs, the available space in such regions is extremely limited.
Thus, some of the above issues may be at least partly addressed by an engine cylinder head coupled to a cylinder, comprising an intake duct having a wall, and a rotatable valve, wherein a cross-section of the valve has a first surface with greater curvature than a second surface. In a first position, the second surface aligns with a curve in the wall, and in a second position, the first surface and the second surface protrude into the duct and form a step at the wall. In one example, the first position allows airflow through the intake duct with a reduced obstruction, since the second surface aligns with the curved wall of the intake duct. This first position of the valve may be used during high load/speed in an engine to increase airflow efficiency, and thus increase peak torque of the engine. In the second position, the first surface and the second surface may create a downstream step in the intake duct via their protrusion into the duct, which can increase tumble flow patterns in the intake air and cylinder. Thus, the second position may be used during low engine load/speed to increase the tumble flow. Further, because the valve can rotate between these positions, as well as potentially other positions therebetween or thereafter, a compact engine cylinder head design is achieved.
In one specific example, the rotatable valve is located at a curvature of at air intake duct, which is proximate to the coupling between the intake duct and the cylinder head. Further, the rotatable valve is rotatable around a rotational axis, which lies outside of the intake duct. As such, the rotatable valve is located at a location where airflow is affected by low engine load/speed.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.